1. Field of the Invention
The present invention relates to a rotor structure of an electric rotating machine such as ac generator or electric motor and, more particularly, to a magnet that prevents leakage of magnetic flux from inside diameter face of claw magnetic poles and to a structure of fitting the magnet.
2. Description of the Related Art
In a conventional rotor structure, rectangular solid magnets polarized in a direction of reducing leakage of magnetic flux between sides of adjacent claw magnetic poles are fixed between the claw magnetic poles facing each other, and holders for reducing centrifugal force are used to fit these magnets.
When the magnets for preventing leakage of magnetic flux are fitted to the claw magnetic poles of a rotor core as described above, the claw magnetic poles increase in weight. Therefore, end of each claw magnetic pole reciprocates toward a rotor coil and a stator due to centrifugal force caused by rotation of the rotor and magnetic attraction between the claw magnetic pole and the stator produced at the time of power generation.
As a result, a load is applied to the magnets between the claw magnetic poles, and this sometimes may cause distortion or breakage of the magnets.
To overcome this, in a conventional rotor, a magnet is fixed to each claw magnetic pole in such a manner as to cover an inner circumferential face and a side face of the claw magnetic pole.
In this known construction, spaces are left between the adjacent magnets.
As a result, the claw magnetic poles and the magnets reciprocate independently, therefore any load is not applied to the magnets, and it is possible to prevent the magnets from breakage (for example, see the Japanese Patent Publication (unexamined) No. 1999/136913, pages 3 and 4).
In another conventional rotor, each claw magnetic pole is provided with two ferrite magnets on both side faces of each claw magnetic pole, and these magnets are polarized so as to reduce leakage of magnetic flux between the claw magnetic poles.
These magnets are supported on the claw magnetic poles, with a slant so as to spread their outer circumference sides toward each other, by magnet-holding members for absorbing centrifugal force that acts on the mentioned magnets when the rotor is rotating through deformation of the magnet-holding members themselves. Thus, the magnets are so constructed as to withstand centrifugal force (for example, see the Japanese Patent Publication (unexamined) No. 2001/86715, page 6).
Generally, in order to improve output of a rotor of an electric rotating machine, one method is to reduce an air gap between rotor and stator, and another is to prevent leakage of magnetic flux from magnetic poles.
The easiest method to prevent leakage of magnetic flux from the magnetic poles is fitting a permanent magnet to a portion where magnetic flux leaks, i.e., between the magnetic poles or on the inside diameter face of the claw magnetic poles.
To fix the permanent magnet, it is necessary to use any magnet-holding member, and in a case where the magnets are fitted between the claw magnetic poles, centrifugal force acts on the magnet itself. Therefore, it is necessary that the magnet-holding member be constructed so as to withstand centrifugal force to prevent the magnet from getting out.
In the mentioned prior art, structure of the magnet-holding member is strong enough to withstand centrifugal force by employing a special configuration.
However, a problem exists in this prior art that the magnet-holding member itself increases in weight thereby increasing weight of the claw magnetic poles as a whole, eventually resulting in deformation of the claw magnetic poles.
Another problem exists in prior art that it is essential to enlarge the air gap because of preventing the electric rotating machine from breakage occurring at the time the claw magnetic poles come in contact with the stator.